String Basics and Memory Representation in DSA C# - Build from Scratch

String Basics and Memory Representation

📖 Scenario: Imagine you are working on a simple text editor that needs to handle and display user names correctly. Understanding how strings work and how they are stored in memory is important to manage text efficiently.

🎯 Goal: You will create a string variable, check its length, access characters by index, and print the string and its details to understand how strings are represented in memory.

📋 What You'll Learn

Create a string variable with a specific value

Create an integer variable to store the string length

Access a character at a specific index in the string

Print the string, its length, and the accessed character

💡 Why This Matters

🌍 Real World

Handling user names and text input correctly is important in many applications like chat apps, forms, and games.

💼 Career

Understanding string basics and memory representation helps in debugging, optimizing text processing, and working with APIs that require string manipulation.

1

Create a string variable

Create a string variable called userName and set it to the exact value "Alice".

DSA C#

# Your code here

Hint

Use the string keyword to declare a variable and assign the value with double quotes.

2

Get the length of the string

Create an integer variable called length and set it to the length of the string userName using the Length property.

DSA C#

string userName = "Alice";
# Your code here

Hint

Use userName.Length to get the number of characters in the string.

3

Access a character by index

Create a char variable called firstChar and set it to the first character of userName using index 0.

DSA C#

string userName = "Alice";
int length = userName.Length;
# Your code here

Hint

Use square brackets [] with index 0 to get the first character.

4

Print the string, length, and first character

Print the values of userName, length, and firstChar each on a new line using Console.WriteLine.

DSA C#

string userName = "Alice";
int length = userName.Length;
char firstChar = userName[0];
# Your code here

Hint

Use Console.WriteLine three times to print each value on its own line.

Practice

1. What does the string type in C# represent in memory?

easy

A. A list of integers representing ASCII codes

B. A sequence of characters stored as Unicode values

C. A mutable array of bytes

D. A pointer to a memory address without data

Solution

1. Step 1: Understand string storage in C#

   C# strings store characters as Unicode, allowing international text.

2. Step 2: Compare options with string behavior

   Only A sequence of characters stored as Unicode values correctly describes strings as sequences of Unicode characters.

3. Final Answer:

   A sequence of characters stored as Unicode values -> Option B

4. Quick Check:

   string = Unicode characters [OK]

Hint: Remember C# strings are Unicode sequences, not byte arrays [OK]

Common Mistakes:

• Thinking strings are mutable arrays
• Confusing ASCII with Unicode
• Assuming strings are just pointers

2. Which of the following is the correct way to declare and initialize a string in C#?

easy

A. string s = "hello";

B. string s = hello;

C. string s = 'hello';

D. string s = "hello";
char[] arr = s;

Solution

1. Step 1: Check string literal syntax

   In C#, string literals use double quotes, so "hello" is correct.

2. Step 2: Validate each option

   string s = 'hello'; uses single quotes (for chars), B misses quotes, D tries to assign string to char array directly (invalid).

3. Final Answer:

   string s = "hello"; -> Option A

4. Quick Check:

   Strings use double quotes in C# [OK]

Hint: Use double quotes for strings, single quotes for chars [OK]

Common Mistakes:

• Using single quotes for strings
• Forgetting quotes around text
• Assigning string directly to char array

3. What will be the output of the following C# code?

string s1 = "hello";
string s2 = "hello";
Console.WriteLine(object.ReferenceEquals(s1, s2));

medium

A. true

B. false

C. Compilation error

D. Runtime exception

Solution

1. Step 1: Understand string interning in C#

   String literals with same content are interned and share the same reference.

2. Step 2: Check ReferenceEquals for s1 and s2

   Since both are "hello" literals, ReferenceEquals returns true.

3. Final Answer:

   true -> Option A

4. Quick Check:

   String literals share references = true [OK]

Hint: String literals with same text share references [OK]

Common Mistakes:

• Assuming ReferenceEquals returns false for equal strings
• Confusing value equality with reference equality
• Expecting runtime errors

4. Identify the error in the following C# code snippet:

string s = "test";
s[0] = 'T';
Console.WriteLine(s);

medium

A. Runtime error: index out of range

B. Syntax error: missing semicolon

C. Strings are immutable; cannot assign to s[0]

D. No error; output is "Test"

Solution

1. Step 1: Check string mutability in C#

   Strings are immutable; individual characters cannot be changed by index.

2. Step 2: Analyze assignment to s[0]

   Assigning to s[0] causes a compile-time error because strings cannot be modified this way.

3. Final Answer:

   Strings are immutable; cannot assign to s[0] -> Option C

4. Quick Check:

   Strings immutable = assignment error [OK]

Hint: Remember strings cannot be changed character-by-character [OK]

Common Mistakes:

• Trying to modify string characters directly
• Expecting runtime error instead of compile error
• Assuming strings behave like char arrays

5. Given the following code, what will be the output?

string s = "hello";
string t = s + " world";
Console.WriteLine(s);
Console.WriteLine(t);

Choose the correct output representation.

hard

A. hello world
hello

B. hello world
hello world

C. hello
world

D. hello
hello world

Solution

1. Step 1: Understand string concatenation and immutability

   Concatenation creates a new string; original string s remains unchanged.

2. Step 2: Trace the output statements

   Console.WriteLine(s) prints hello; Console.WriteLine(t) prints hello world.

3. Final Answer:

   hello hello world -> Option D

4. Quick Check:

   Original string unchanged, new string created [OK]

Hint: Concatenation creates new string; original stays same [OK]

Common Mistakes:

• Assuming original string changes after concatenation
• Mixing order of printed strings
• Confusing string references with values